1. Field of the Invention.
The present invention relates generally to pipe aligning devices, and more particularly, by not by way of limitation, to an apparatus for centering a pipe string in a slip bowl disposed in a drilling rig floor to facilitate setting a set of slips about the pipe string.
2. Description of Related Art.
During the drilling, completion and work-over of oil and gas wells, it is necessary to insert into and remove from the well bore a string of pipe (e.g., drill string, casing string, or tubing string). Whether forming the string or breaking the string apart, the pipe string is suspended from the rig floor as additional sections of pipe are either added to or removed from the string. Suspension of the string from the rig floor is accomplished in a manner well known in the art by the use of a slip and bowl set.
The bowl is disposed in the rig floor and includes an internal tapered surface. The slips, on the other hand, include a serrated inner surface and an external tapered surface whereby the slips are wedged between the pipe and the slip bowl when the internal surface of the slips grippingly engage the pipe thereby supporting the pipe from the rig floor. The slips are disposed about the pipe string while the pipe string is suspended from an elevator provided on the rig for hoisting and lowering pipe. Slip designs include both manual slips and power slips. Manual slips, which are constructed of a plurality of hinged slip segments, are manually disposed between the pipe and the slip bowl, while power slips are automatically disposed about the pipe with either spring, pneumatic or hydraulic power.
A problem often encountered when attempting to position both manual slips and power slips about the pipe string is that the string is not centered in the slip bowl due to a variety of variables including the fact that the elevator is typically not centered directly over the slip bowl. This misalignment of the pipe relative to the slip bowl causes placement of the slips around the pipe whereby the slips can engage the pipe to be difficult. With manual slips, the center slip segment can often be forcibly wedged between the pipe and the slip bowl when the pipe string is misaligned, and in turn, dragged into the slip bowl by the weight of the pipe. However, this can result in significant damage being incurred to the pipe, the slips and the slip bowl. Power slips are designed primarily to work on and around the center line of the slip bowl and it is generally not possible to position the slips so that the slips can be wedged between the pipe and the bowl when the pipe string is misaligned.
To this end, a need exists for an apparatus for centering a string of pipe in a slip bowl disposed in a drilling rig floor to facilitate setting the slips about the pipe string prior to attempting to set the slip in the bowl. It is to such an apparatus that the present invention is directed.